Anders Behring Breivik, the man accused of the murder of at least 92 Norwegians in a bomb and gun massacre, boasted online about his discussions with the far-right English Defence League and other anti-Islamic European organisations.

The Norwegian prime minister, Jens Stoltenberg, said Norwegian officials were working with foreign intelligence agencies to see if there was any international involvement in the slaughter. "We have running contact with other countries' intelligence services," he said.

Breivik was arrested on Utøya island where he shot and killed at least 85 people, mostly teenagers, at a youth summer camp for supporters of Norway's Labour party after bombing Oslo's government district just hours before. Dressed as a police officer, he ordered the teenagers to gather round him before opening fire. Survivors described how dozens of people were mown down. The massacre led to the largest death toll ever recorded by a single gunman on the rampage.

Ida Knudsen, 16, said she had been in a group of 100 who had initially run from the killer, but that was reduced to about 60 as the gunman pursued them. Eventually she was one of 12 who climbed into a boat and escaped.

Another survivor, 15-year-old Mattori Anson, described how he fled into a cabin with 40 other teenagers. They blocked the door and the killer tried to get inside. "Then he began shooting at the door." Eventually he gave up and the occupants all survived.

With the entire island a crime scene, officers were still combing the shoreline on Saturday and boats were searching the water for more bodies amid fears the toll could rise further. Police were continuing to investigate whether there had been a second gunman on the island.

The disclosure of Breivik's claimed links with far-right organisations came as details continued to emerge about the rightwing Christian fundamentalist and Freemason behind Norway's worst postwar act of violence.

It was revealed that the 32-year-old former member of the country's conservative Progress party – who had become ever more extreme in his hatred of Muslims, leftwingers and the country's political establishment – had ordered six tonnes of fertiliser in May to be used in the bombing. While police continued to interrogate Breivik, who was charged with the mass killings, evidence of his increasingly far-right world-view emerged from an article he had posted on several Scandinavian websites, including Nordisk, a site frequented by neo-Nazis, far-right radicals and Islamophobes since 2009.

The Norwegian daily VG quoted one of Breivik's friends, saying that he had become a rightwing extremist in his late 20s and was now a strong opponent of multiculturalism, expressing strong nationalistic views in online debates.

Breivik had talked admiringly online about conversations he had had with unnamed English Defence League members and the organisation Stop the Islamification of Europe (SIOE) over the success of provocative street actions leading to violence.

"I have on some occasions had discussions with SIOE and EDL and recommended them to use certain strategies," he wrote two years ago. "The tactics of the EDL are now to 'lure' an overreaction from the Jihad Youth/Extreme-Marxists, something they have succeeded in doing several times already."

Contacted by email, the EDL had not answered.

The latest disclosures came as the Norwegian prime minister, Jens Stoltenberg, flew by helicopter to a hotel in the town of Sundvollen – close to the island of Utøya – where many survivors were taken and where relatives converged to reunite with loved ones or identify their dead.

"A whole world is thinking of them," Stoltenberg said, his voice cracking with emotion. He said the twin attack made Friday the deadliest day in Norway's peacetime history. "This is beyond comprehension. It's a nightmare. It's a nightmare for those who have been killed, for their mothers and fathers, family and friends."

Buildings around the capital lowered their flags to half-mast while people streamed to Oslo cathedral to light candles and lay flowers. Outside, mourners began building a makeshift altar from dug-up cobblestones. On Saturday the Queen wrote to Norway's King Harald to offer her condolences and express her shock and sadness.

Breivik's Facebook page was blocked, but a cached version describes a conservative Christian from Oslo. The profile veers between references to lofty political philosophers and gory popular films, television shows and video games. The account appears to have been set up on 17 July. The site lists no "friends" or social connections.